A modern enterprise needs to store an increasing number of important files. In order to meet a demand of the enterprise for a query of the important files and meet requirements of related storage regulations for file auditing, an increasing number of storage systems support a write once read many (WORM) function. For a file specified by a user, a storage system that supports the WORM function can set a term of protection, within which a security attribute of the file is usually set to a read-only attribute. Within the term of protection, the file can only be read but cannot be modified or deleted. The security attribute of the file can be modified or deleted according to a demand of the user only when the term of protection of the file expires. In addition, generally, the user cannot modify the set term of protection within the term of protection of the file, so as to maximally ensure security of the file.
The term of protection of the file is closely associated with a system time of the storage system. The term of protection of the file is calculated according to the system time of the storage system. If the system time of the storage system is maliciously changed, an actual term of protection of the file is changed, and the security attribute and file content of the file may be changed, which further affects the security of the file.
In the prior art, in order to ensure that a storage system has a reliable system time, a real-time clock (RTC) is usually integrated into a southbridge chip of a controller in the storage system. The RTC refers to an electronic device that can output actual time like a clock. Generally, the RTC may be an integrated circuit and therefore can also be called a clock chip. The RTC can generally be applied to a system that needs accurate time, such as a personal computer, a server, a storage system, or an embedded system. When a processor in the controller in the storage system is powered on, the processor reads time of the RTC that is integrated into the southbridge chip and uses the time of the RTC as the system time of the storage system. In the prior art, however, an intruder can easily achieve an objective of modifying the system time of the storage system by modifying the time of the RTC that is integrated into the southbridge chip, so as to achieve an objective of modifying a term of protection of a file, which affects security of the file.